Nonaqueous electrolyte secondary batteries such as lithium secondary batteries are being actually used in various applications ranging from power supplies for so-called consumer products such as mobile phones and notebook computers, to drive power supplies for vehicles such as automobiles. There have recently been increasing demands on higher performances for the nonaqueous electrolyte secondary batteries. In particular, enhancements are desired in various battery characteristics such as high capacity, low-temperature service characteristics, high-temperature storage characteristics, cycle characteristics and overcharge safety.
Electrolytic solutions used in the nonaqueous electrolyte secondary batteries are usually composed of electrolytes and nonaqueous solvents as the main components. Examples of the main nonaqueous solvents include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; and cyclic carboxylate esters such as γ-butyrolactone and γ-valerolactone.
A number of studies have been carried out on nonaqueous solvents, electrolytes and additives in order to improve characteristics of nonaqueous electrolyte secondary batteries such as load characteristics, cycle characteristics, storage characteristics and overcharge safety.
Patent Literatures 1 to 10 propose that aromatic esters such as methyl benzoate, ethyl benzoate, phenyl propionate, phenyl acetate and benzyl acetate are added to electrolytic solutions in order to enhance properties of batteries such as energy density, long-term durability, small generation of gas during high-temperature storage and low-temperature characteristics.
Patent Literature 11 proposes a technique directed to enhancing the safety of batteries during overcharging by the use of an electrolytic solution containing a specific carboxylic aromatic ester.
Patent Literature 12 proposes a technique in which a specific carboxylic aromatic ester compound is added to a nonaqueous electrolytic solution in order to prevent the swelling of batteries during high-temperature storage without causing a decrease in battery capacity.